Journal and pilot bearings with alternating surface areas of wear resistant and anti-galling materials

ABSTRACT

The journal and/or pilot bearings of a rotary cone earth boring bit are constructed to include alternating areas of wear resistant materials and anti-galling materials. The bearing matrix is formed by compressing a powdered alloy in the shape of the desired bearing element. The bearing matrix is sintered, thereby forming a porous bearing element. An anti-galling material is infiltrated into the porous matrix of the bearing element and the bearing element is hardened. The resulting bearing element includes areas of water resistant materials and areas of anti-galling materials.

This is a division of application Ser. No. 706,338, filed July 19, 1976and now U.S. Pat. No. 4,105,263, issued Aug. 8, 1978, which was adivision of application Ser. No. 395,880 filed Sept. 10, 1973 and nowU.S. Pat. No. 3,984,158, issued Oct. 5, 1976.

BACKGROUND OF THE INVENTION

The present invention relates to bearing systems and, more particularly,to journal and pilot bearings with improved performance and longerlifetime characteristics. The bearing system of the present invention isespecially adapted for use on that type of rock bit popularly known as athree cone bit; however, its use is not restricted thereto and thebearing system of the present invention can be used in other equipmentwherein an improved bearing system is required.

A rotary rock bit must operate under very severe environmentalconditions and the size and geometry of the bit is restricted by theoperating characteristics. At the same time, the economics of petroleumproduction demand a longer lifetime and improved performance from thebit. In attempting to provide an improved bit, new and improvedmaterials have been developed for the cutting structure of the conesthereby providing a longer useful lifetime for the cones. This hasresulted in the bearing system being first to fail during the drillingoperation. Consequently, a need exists for an improved bearing system toextend the useful lifetime of the bit.

In order to obtain high penetration rates with a rotary rock bit in someformations, it is necessary to apply heavy loads on the bit and tooperate the bit at a moderate speed. With other formations only moderateloads are required but the bit must be operated at relatively highspeeds. The rock bit operates under a highly corrosive environment andis subjected to temperature extremes. The drilling operation may beconducted thousands of feet underground wherein elevated temperaturesare encountered. The bit is continually flushed by a circulatingdrilling fluid to cool the bit and carry away the drill cuttings. Thisfluid is generally water with chemicals added to control water loss orto control viscosity and/or pH. Some of these chemicals may result in acorrosive drilling fluid. The drilling cuttings, the materialsencountered in the earth formations, barites added for fluid weightcontrol, and the chemical composition of the drilling fluid combine tocreate a corrosive and abrasive drilling environment.

The bit is subjected to a wide range of fluid pressures during thedrilling operation. When the bit is at the surface, it is of course onlysubjected to atmospheric pressure; however, when lowered into the wellbore, it will be exposed to very high fluid pressure because of the headof the fluid in the well bore. In view of the circumstances explainedabove, it can be appreciated that a bearing system for a rotary rock bitmust include exceptional performance characteristics in a limitedgeometrical configuration. Since the entire drill string must bewithdrawn to replace the bit when it fails, it is highly desirable tohave the bearing system operate for an extended period of time.

DESCRIPTION OF THE PRIOR ART

In U.S. Pat. No. 2,595,903 to K. H. Swart, patented May 6, 1952, a threecone rock bit is shown. The bit includes three shanks which areassembled together to form the bit. The lower end of each shank isformed into a journal and a generally conical tooth cutter is receivedover the journal. The bearing system includes friction-type bearings andanti-friction bearings. This patent sets out some of the problemsencountered with rotary rock bits.

In U.S. Pat. No. 3,235,316 to J. R. Whanger, patented Feb. 15, 1966, ajournal bearing for a rock bit is shown with alternating surface areasof wear-resistant and anti-galling materials. The bearing systemdisclosed in this patent includes grooves in one of the rotatablemembers with a soft metal having anti-galling characteristics positionedin the grooves.

In U.S. Pat. No. 2,096,252 to R. P. Koehring, patented Oct. 19, 1937, aporous bearing is formed by "briquetting" metal powders under highpressure. The porous bearing is sintered to form a rigid, porousstructure. The sintered porous metal bearing is then subjected to aninfiltration process wherein molten lead is absorbed by capillary actioninto the porous structure. The metal forming the porous bearing matrixstructure may be copper, bronze, or brass.

In U.S. Pat. No. 2,706,693 to J. Haller patented Apr. 19, 1955, aprocess of impregnating metal bearings is shown. The bearing is formedby "briquetting" or pressing powdered iron to form the porous structure.The pressed bearing body is then subject to a process wherein sinteringand infiltration occur simultaneously. The infiltration is accomplishedduring the sintering operation by the insertion of a core of copper orcopper zinc alloy into the center of the bearing body. The copper insertmelts and infiltrates into the pores of the powdered iron body leavingin its place a central void or cavity. The bearing body is thensubjected to a second infiltration step where an antimony is"reinfiltrated" into the bearing structure. The "reinfiltrating metal"may be a mixture of antimony and lead, antimony and tin, lead and tin,lead alone, or tin alone.

SUMMARY OF THE INVENTION

The present invention provides a novel bearing system for earth boringbits. At least one of the bearing surfaces includes areas of wearresistant material and areas of anti-galling material. An alloy powderis compressed into the shape of the desired bearing element, therebyproviding a porous matrix. The porous matrix is sintered. Ananti-galling material is infiltrated into the porous matrix. The porousmatrix is hardened, thereby providing a bearing element with a hard wearresistant surface having pores infiltrated with anti-galling material.The above and other features and advantages of the present inventionwill become apparent from a consideration of the following detaileddescription of the invention when taken in conjunction with thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial view of a three cone rotary rock bit.

FIG. 2 illustrates one-third of a three cone rotary rock bit,incorporating a bearing constructed in accordance with the presentinvention.

FIG. 3 illustrates a porous matrix of a bearing element.

FIG. 4 is an enlarged view of a section of the porous matrix shown inFIG. 3.

FIG. 5 is an enlarged view of the porous matrix shown in FIG. 3, afterit has been case hardened.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a three cone jet-type rotary rock bit is shown andgenerally designated by the reference number 10. The bit 10 includes abit body 11 including an upper threaded portion 12. The threaded portion12 allows the bit 10 to be connected to the lower end of a rotary drillstring (not shown). Depending from the bit body 11 are threesubstantially identical arms with two of the arms 13 and 13' being shownin FIG. 1. Three rotary cone cutters, 14, 14' and 14" are rotatablypositioned on three bearing pins extending from the arms. Each of thecutters 14, 14' and 14" includes cutting structures 15, 15' and 15",respectively, on its outer surface adapted to disintegrate theformations as the bit 10 is rotated and moved through the formations.The cutting structure 15, 15' and 15" is shown in the form of tungstencarbide inserts; however, it is to be understood that other cuttingstructures, such as steel teeth, may be used as the cutting structure onthe cone cutters.

The bit 10 includes a central passageway 16 extending along the centralaxis of body 11 to allow drilling fluid to enter from the upper sectionof the drill string (not shown) immediately above and pass downwardthrough three jet nozzles, one nozzle 17 being shown in FIG. 1, to thebottom of the well bore. In use, the bit 10 is connected as the lowermember of a rotary drill string (not shown) and lowered into a well boreuntil the cone cutters 14, 14' and 14" engage the bottom of the wellbore. Upon engagement with the bottom of the well bore, the drill stringis rotated, rotating bit 10 therewith. The cone cutters 14, 14' and 14"rotate on their respective bearing pins. Drilling fluid is forceddownward through the interior passage of the rotary drill string and thedrilling fluid continues through the central passageway 16 of bit 10passing through the nozzles to the bottom of the well bore, thenceupward in the annulus between the rotary drill string and the wall ofthe well bore to the earth's surface.

A cut-away view of one of the arms 13 of a bit incorporating a bearingsystem constructed in accordance with the present invention is shown inFIG. 2. The bit is adapted to be connected to a rotary drill string andoperates in the manner previously described. The elongated lower portionof arm 13 forms a journal 18 and the shell 19 of rotatable cutter 14 ismounted upon journal 18. Positioned on the exterior surface of rotatablecutter 14 is the cutting structures 15. The cutting structures 15consist of a series of tungsten carbide inserts. As the bit is rotated,the inserts contact and disintegrate the formations to form the earthborehole.

The bearing system constructed in accordance with the present inventioninsures free rotation of rotatable cutter 14 under the severe drillingconditions. A series of ball bearings 20 insure that the shell 19 ofcutter 14 is rotatably locked on journal 18. The rotatable cutter 14 ispositioned upon journal 18 and the series of ball bearings 20 insertedthrough a bore 21 extending into arm 13. After the ball bearings 20 arein place, plug 22 is inserted in bore 21 and welded therein by weld 23.

Journal 18 and arm 13 are also provided with a passage 24 to channellubricant from a lubricant reservoir 25 to the areas between the variousbearing surfaces. Passage 24 intersects bore 21 and plug 22 is ofreduced diameter in this area to allow the lubricant to be channeled tothe bearings. Additional passages 26, 27, and 28 allow the lubricant tobe channeled from bore 21 to the bearings. Lubricant reservoir 25 isfilled with a lubricant containing entrained particles of anti-gallingmaterial and a cap 29 locked in place on arm 13 to retain the lubricantin reservoir 25. Cap 29 is constructed so that a passage 30 communicatesthe interior of reservoir 25 with the outside of the bit. This allowspressure equalization and prevents pressure differentials from damagingthe bearing system. A flexible diaphragm 31 serves to hold the lubricantin position and at the same time provides compensation for pressurechanges.

The lubricant fills reservoir 25, passage 24, bore 21, additionalpassages 26, 27, and 28, and the spaces between the cutter shell 19 andjournal 18. A flexible seal 32 contacts cutter shell 19 and forms a sealbetween cutter shell 19 and journal 18 to prevent loss of lubricant orcontamination of the lubricant from materials in the well bore. Asexplained above, pressure on the lubricant is equalized by cap 29 anddiaphragm 31 and the lubricant is not lost or contaminated during thedrilling operation. As the bit is lowered into the well bore, it will besubjected to increasing fluid pressure the deeper it goes. If means hadnot been provided for equalizing the pressure on the lubricant, thepressure differential across seal 31 would be sufficient to rupture it.

Positioned in the inner surface of the shell 19 of cone cutter 14 is ajournal bearing bushing 33 and a pilot bearing bushing 34. A thrustbutton 35 is positioned in the nose of the shell 19. The bushings 33 and34 and the thrust button 35 are locked in cutter shell 19 by forcefitting. The bearing surface areas of bushings 33 and 34 and thrustbutton 35 contain surfaces having alternating areas of wear resistantand anti-galling materials. The bearing surfaces have a hard wearresistant matrix with high strength and the self lubrication of theanti-galling material. The useful lifetime of the bearings are extended,thereby extending the useful lifetime of the bit.

Referring now to FIG. 3, the porous matrix 36 used for the pilot bearingbushing 34 is shown. The porous matrix 36 is formed by pressing an alloypowder into the shape of the desired bearing element. The alloy powderchosen for the porous matrix 36 is a low carbon nickel steel alloypowder consisting of AISI 4600 100 mesh particles. It is to beunderstood that other alloy powders can be used for the porous matrix 36such as stainless steel particles.

Graphite or carbon is mixed with the alloy powder prior to pressing toobtain the desired final carbon content. For example, sufficientgraphite is added to the alloy powder to provide the porous matrix 36with 0.4% carbon content after the pressed matrix is sintered. A dielubricant is generally added to the alloy powder to lubricate the dieand increase the green strength of the matrix prior to pressing. The dielubricant may, for example, be zinc stearate. The die lubricant burnsoff during sintering. The alloy powder is pressed using a force of 35-40tons per square inch (cross-sectional area). This will provide theporous matrix 36 with an apparent density of 6.8 grams per cubiccentimeter (85-87% theoretical density) after sintering. Other densitiesare contemplated by the present invention and the density may generallybe within the range of 50-95% theoretical density.

The porous matrix 36 is sintered at 2050° F. for forty minutes. Thegraphite mixed with alloy powder diffuses into the steel during thesintering and combines with the steel to produce a homogeneous structurewith the desired carbon content. Diffusion of the carbon throughout thestructure as well as diffusion bonding of the particles togetherrequires temperatures above 1800° F. This diffusion process may takeseveral hours at 1800° F. while taking less than one hour attemperatures above 2000° F. An enlarged view of a section of the porousmatrix 36 is shown in FIG. 4. The porous matrix 36 contains amultiplicity of pores 37. Approximately 95% of the voids or pores 37left in the matrix 36 are interconnected and can be filled with ananti-galling material by infiltration.

The porous matrix 36 is infiltrated with 85% silver--15% manganese alloyat a temperature of 2050° F. for forty minutes. The silver manganesealloy is placed on the porous matrix 36 and the heat is applied to allowcapillary action and gravity to draw the silver into and fill the pores37. It is to be understood that other anti-galling materials may be usedas the infiltrating material. In general, the infiltrating material canbe a metal or alloy having softness and anti-galling nature on the orderof silver, silver alloys or babbit metals. Approximately 95% of thepores 37 are filled with silver.

After the porous matrix 36 has been infiltrated with silver the matrix36 is hardened. The hardening may consist of through hardening or casehardening. The porous matrix 36 of the preferred embodiment is casehardened by pack carburizing at 1700° F. for twelve hours, heating to1470° for one and one-half hours and quenching in an oil bath. Thematrix 36 is then tempered and machined into the specific shape of thedesired bearing element.

Referring to FIG. 5, an enlarged view of a section of the porous matrix36 is shown after the porous matrix has been case hardened. Asubstantial number of the pores 37 have been filled with the silvermanganese anti-galling material. The case hardening step has made thesurface 37 of the porous matrix 36 hard and wear resistant. The pores 37at the surface containing the softer anti-galling material provide areason the surface 38 that consist of an anti-galling material. The matrixmaterial 36 has an apparent hardness greater than Rockwell C 20 whereasthe surface 38 has an apparent hardness greater than Rockwell C 40.

I claim:
 1. A method of providing an improved bearing system in an earthboring bit, said bearing system including a journal and a rotatablecutter positioned to rotate about said journal with a bearing elementbetween said rotatable cutter and said journal, comprising the stepsof:pressing an alloy powder into the general shape of said bearingelement, thereby producing a porous matrix element, sintering saidporous matrix element, infiltrating an anti-galling material into saidporous matrix element substantially throughout said porous matrixelement, hardening said porous matrix element, and machining said porousmatrix element into the specific shape of said bearing elementassembling said bearing element between said rotatable cutter and saidjournal.
 2. The method of claim 1 wherein said step of hardening saidporous matrix element consists of case hardening said matrix element. 3.The method of claim 1 wherein said alloy powder is a ferrous alloypowder.
 4. The method of claim 1 wherein said alloy powder is astainless steel alloy powder.
 5. The method of claim 1 including thestep of adding carbon to said alloy powder prior to pressing the alloypowder into the general shape of the desired bearing element.
 6. Themethod of claim 5 wherein the amount of carbon added to said alloypowder is sufficient to provide the porous matrix element with a carboncontent after sintering within the range of 0.04% to 1.5%.
 7. A methodof providing an improved bearing system in an earth boring bit, saidbearing system including a journal and a rotatable cutter positioned torotate about said journal with a bearing element between said rotatablecutter and said journal, comprising the steps of:mixing graphite with aferrous alloy powder, pressing said mixture of a ferrous alloy powderand graphite into the general shape of said bearing element therebyproducing a porous matrix element, sintering said porous matrix element,infiltrating an anti-galling material into said porous matrix elementsubstantially throughout said porous matrix element, hardening saidporous matrix element, and machining said porous matrix element into thespecific shape of said bearing element assembling said bearing elementbetween said rotatable cutter and said journal.
 8. The method of claim 7wherein said step of hardening said porous matrix element consists ofcase hardening said matrix element.
 9. The method of claim 7 whereinsaid ferrous alloy powder is a stainless steel alloy powder.
 10. Themethod of claim 7 wherein the amount of graphite added to said alloypowder is sufficient to provide the porous matrix element with a carboncontent after sintering within the range of 0.04% to 1.5%.